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rcu: Add full-sized polling for get_state()

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The get_state_synchronize_rcu() API compresses the combined expedited and
normal grace-period states into a single unsigned long, which conserves
storage, but can miss grace periods in certain cases involving overlapping
normal and expedited grace periods.  Missing the occasional grace period
is usually not a problem, but there are use cases that care about each
and every grace period.

This commit therefore adds the next member of the full-state RCU
grace-period polling API, namely the get_state_synchronize_rcu_full()
function.  This uses up to three times the storage (rcu_gp_oldstate
structure instead of unsigned long), but is guaranteed not to miss
grace periods.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney
2022-07-28 19:58:13 -07:00
parent 91a967fd69
commit 3fdefca9b4
4 changed files with 46 additions and 4 deletions
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6
include/linux/rcutiny.h
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@@ -19,6 +19,12 @@ struct rcu_gp_oldstate {
};
unsigned long get_state_synchronize_rcu(void);
static inline void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
{
rgosp->rgos_norm = get_state_synchronize_rcu();
}
unsigned long start_poll_synchronize_rcu(void);
bool poll_state_synchronize_rcu(unsigned long oldstate);